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United States Department of Agriculture

Agricultural Research Service

Research Project: Biology and Control of Human Pathogens on Fresh Produce

Location: Produce Safety and Microbiology Research

Title: Diversity of pulsed field gel electrophoresis pulsotypes, serovars and antibiotic resistance among Salmonella isolates from wild amphibians and reptiles in the California central coast

Authors
item GORSKI, LISA
item Jay-Russell, Michele -
item LIANG, ANITA
item WALKER, SAMARPITA
item Bengson, Yingija -
item Govoni, Jessica
item Mandrell, Robert

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 2013
Publication Date: June 1, 2013
Citation: Gorski, L.A., Jay-Russell, M., Liang, A.S., Walker, S., Bengson, Y., Govoni, J.A., Mandrell, R.E. 2013. Diversity of pulsed field gel electrophoresis pulsotypes, serovars and antibiotic resistance among Salmonella isolates from wild amphibians and reptiles in the California central coast. Foodborne Pathogens and Disease. 10:540-548.

Interpretive Summary: A survey was done of wild amphibians and reptiles along a leafy green-growing region of the Central California Coast to determine the potential for pre-harvest contamination of produce. Samples from 460 amphibians and reptiles and 114 of water samples were collected and cultured for Salmonella. Among the animals sampled were 331 frogs, 59 lizards, 5 newts, 6 salamanders, 39 snakes, and 20 toads. Water (total of 119) samples were taken from the ponds in which the animals were found. Salmonella was isolated from 37 individual animals, including frogs, lizards, snakes, and toads. Snakes were the most likely to contain Salmonella with 57.5% testing positive followed by 15.3% of lizards, 5% of toads, and 1.2% of frogs. Sixteen water samples (14%) were positive. Nineteen different serotypes were identified with the majority of strains being S. enterica subsp. diarizonae, although strains of subsp. enterica, arizonae, and salmae were also found. This subtype of Salmonella is often found associated with reptiles. The serotype isolated most frequently was S. enterica subsp. diarizonae III_16:z10:e,n,x,z15, from snakes and frogs in five different locations in the region. S. enterica subsp. enterica isolates of serotypes Typhimurium and I_6,8:d:- were isolated from water, and strains of S. enterica subsp. enterica Duisburg and its variants were found in animals and water. Genomic analysis indicated that some strains could persist in the environment. Fifty strains displayed antibiotic resistance with 25 strains being resistant to more than one antibiotic. Twenty-one strains were resistant to more than one class of antibiotic and 6 strains were resistant to three classes, including one strain of S. enterica subsp. diarizonae isolated from snake being resistant to five different antibiotics. While these subspecies of arizonae and diarizonae may be less likely to cause human illness, they may serve as reservoirs of antibiotic resistance determinants in the environment, and be sources of contamination of leafy greens associated with product recalls.

Technical Abstract: A survey of cold-blooded vertebrates and associated surface waters in a produce-growing region on the Central California Coast was done between May and September, 2011 to determine the diversity of Salmonella strains in these habitats and individuals. Samples from 460 amphibians and reptiles and 119 of water samples were collected and cultured for Salmonella. Animals sampled were frogs (n=331), lizards (n=59), newts (n=5), salamanders (n=6), snakes (n=39), and toads (n=20). Salmonella was isolated from 37 individual animals, including frogs, lizards, snakes, and toads. Snakes were the most likely to contain Salmonella with 59% testing positive followed by 15.3% of lizards, 5% of toads, and 1.2% of frogs. Fifteen water samples (12.6%) were positive. Nineteen different serotypes were identified with the majority of strains being S. enterica subsp. diarizonae, although strains of subsp. enterica, arizonae, and salmae were also found. The serotype isolated most frequently was S. enterica subsp. diarizonae III_16:z10:e,n,x,z15, from snakes and frogs in five different locations in the region. S. enterica subsp. enterica isolates of serotypes Typhimurium and I_6,8:d:- were isolated from water, and strains of S. enterica subsp. enterica Duisburg and its variants were found in animals and water. Some samples contained more than one type of Salmonella strain. Analysis of pulsed field gel electrophoresis pulsotypes indicated some strains persisted in environments over the course of the study. Fifty strains displayed antibiotic resistance with 25 strains being resistant to more than one antibiotic. Twenty-one strains were resistant to more than one class of antibiotic and 6 strains were resistant to three classes, including one strain of S. enterica subsp. diarizonae isolated from snake being resistant to five different antibiotics. While these subspecies of arizonae and diarizonae may be less likely to cause human illness, they may serve as reservoirs of antibiotic resistance determinants in the environment, and be sources of contamination of leafy greens associated with product recalls.

Last Modified: 9/29/2014
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